The stakes are considerable. Tillage is among the most energy-intensive operations in crop production, and improper machinery use during land preparation can irreversibly damage soil structure. Deep ploughing demands enormous power to fracture compacted horizons, which is why manufacturers have developed machines that pair a passive subsoiler shank with an active, powered rotary tiller. The rotary component pulverizes the soil the subsoiler cracks open, mixes in fertilizer, crop residues and organic amendments, and reduces the number of field passes needed. Fewer passes mean less compaction, less fuel, less labor and less time in the field. But until now, designers have lacked a reliable way to predict exactly what such combined implements do to the soil profile before the steel ever touches the ground.

DEM offers that window. The technique, pioneered in the geotechnical literature since the late 1970s, treats soil not as a continuous medium but as millions of individual particles, solving the equations of motion for each one as they collide, slide and cohere. In this study, the team modeled the soil bed in Altair EDEM 2022 software using the hysteretic spring with linear cohesion contact model, which adds a cohesion resistance to the normal contact forces between particles to mimic the behavior of real clay. The implement itself was designed in PTC Creo Parametric 3D modeling software and imported into the simulation environment, allowing the researchers to replicate the exact geometry of the subsoiler-cum-rotary tiller used in physical tests.

Calibration was the critical step. Because no universally accepted procedure exists for selecting the micromechanical parameters that govern particle interactions, the team anchored their model to laboratory measurements. They worked with clay soil from the experimental soil bin at Nanjing Agricultural University, containing 47.0 percent clay, 36.5 percent silt and 15.5 percent sand, with an average bulk density of 1.5 grams per cubic centimeter. Direct shear tests under unconsolidated undrained conditions yielded cohesion, internal friction angle and shear strength via the Mohr-Coulomb equation, while a digital penetrometer measured penetration resistance at ten locations. Using the angle of repose method and reverse parametrization, the researchers iteratively adjusted restitution and friction coefficients until the simulated soil formed a natural pile at 36.87 degrees, matching the physical material’s behavior.

The validation results are striking. Across eighteen soil bin experiments, the mean horizontal tillage resistance measured by sensors on the three-point linkage of a motorized trolley was 1,950.474 newtons, while vertical resistance averaged 295.92 newtons. The DEM model reproduced these values with a relative error of just 0.4 percent for horizontal resistance and 4.9 percent for vertical resistance. Horizontal resistance predictions achieved a coefficient of determination of 0.9997 with a normalized root mean square error of 0.04, while vertical resistance reached an R-squared of 0.9. An unpaired t-test found no statistically significant difference between simulated and measured values for either component, meaning the virtual experiment was statistically indistinguishable from the real one.

The model also predicted the shape of the furrow left behind. Soil profilometer measurements of the tilled profile matched the simulation with a relative error of 4.3 percent, an R-squared of 0.9936 and a normalized RMSE of 0.23. Both experiment and simulation produced U-shaped furrows with loose soil at the bottom, a profile considered favorable for seed coverage. The average top width of the soil profile was 0.405 meters in the soil bin versus 0.3875 meters in the simulation, and bottom widths were 0.26 and 0.25 meters respectively, a close correspondence that underscores the model’s fidelity.

Perhaps the most consequential finding concerns soil mixing. By coloring the simulated topsoil and subsoil particles differently, the researchers could watch, in effect, inside the soil as the machine passed through. The L-shaped rotary blades promoted predominantly horizontal and downward soil movement with limited upward throw, allowing topsoil particles to migrate toward deeper layers without wholesale inversion of the profile. Even at a tillage depth of 30 centimeters, the natural layering remained discernible, a critical advantage over conventional rotary systems that churn the profile indiscriminately. The mixing of the two layers increased with cutting depth, as expected given the larger soil volume involved, but the vertical-axis rotation design avoided dragging subsoil to the surface, preserving stratification that underpins fertility and moisture retention.

The study also mapped how operating parameters drive energy demand. Both horizontal and vertical resistance rose as tillage depth increased from 0.15 to 0.30 meters, because deeper operation cuts, disperses and moves a greater volume of soil. Resistance likewise grew when forward speed increased from 1.5 to 2.5 kilometers per hour, since faster-moving soil particles gain acceleration, raising normal loads on the tool and thus frictional resistance. The substantial gap between horizontal and vertical forces, roughly 1,800 to 2,060 newtons versus 264 to 323 newtons, shows that far more energy is spent dragging the implement forward than penetrating downward. Notably, the rotary tiller’s rotational motion generated a forward thrust component that offset part of the draft requirement, one reason combined active-passive implements outperform conventional systems in energy efficiency.

The practical implications reach from the design office to the farm field. For manufacturers, the validated model provides a virtual testing platform to optimize blade shape, operating depth and rotational speed across diverse soil conditions without costly physical prototyping. The evidence points toward vertical-axis rotary tillers equipped with L-shaped blades as the configuration of choice for deep tillage that respects soil architecture. For farmers, the combined implement approach promises reduced operational time and fuel consumption while maintaining soil quality, addressing economic and environmental goals simultaneously. As the authors conclude, DEM can serve as an accurate, consistent and fast method for predicting the final soil condition and the resistances required for tillage operations, and with proper blade selection, deep tillage and soil structure conservation need no longer be opposing goals.

Subject of Research: Discrete element simulation of rotary mixing effects on soil structure and tillage resistance for a combined subsoiler and rotary tiller

Article Title: Evaluation of rotary mixing effects on soil structure and tillage resistance using discrete element method

Article References: Makange, N. R., & Ji, C. (2026). Evaluation of rotary mixing effects on soil structure and tillage resistance using discrete element method. Discover Soil, 3(1), Article 148. https://doi.org/10.1007/s44378-026-00308-8

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00308-8

Keywords: discrete element method, tillage resistance, rotary tiller, subsoiler, soil structure, soil bin experiments, EDEM simulation, blade geometry, deep tillage, soil profile, precision agriculture, soil-tool interaction

The study, published in Agricultural Ecology and Environment, addresses a major challenge for farmers working with albic soils. These soils often have high bulk density, limited pore space and weak organic-matter reserves, conditions that restrict root growth, water movement and nutrient cycling. Their compacted structure can also make it difficult for carbon-rich plant residues to enter and remain in deeper layers. At the same time, intensive ploughing can expose protected organic matter to oxygen and accelerate its decomposition, releasing carbon dioxide into the atmosphere.

The researchers tested whether combining different tillage systems with microbial organic fertilizer could overcome these limitations. The field experiment was conducted between 2023 and 2024 in maize-growing soil in Shulan, Jilin Province, northeastern China. The team compared no-tillage, plough tillage and rotary tillage, while applying microbial organic fertilizer at rates of 600, 1,200 or 2,400 kilograms per hectare. Straw-return treatments were also included, and no-tillage without straw return served as the control. The fertilizer was made from composted livestock and poultry manure and contained beneficial microorganisms including Bacillus subtilis, Bacillus amyloliquefaciens and Trichoderma harzianum.

The physical arrangement of each treatment was central to the experiment. Under no-tillage, the straw and fertilizer remained on the soil surface as a protective mulch. Ploughing incorporated these materials to a depth of 40 centimetres, while rotary tillage mixed them into the upper 15 centimetres. After the maize harvest, soil was collected from the 0–20 and 20–40 centimetre layers. Researchers then measured SOC, microbial biomass carbon, bulk density, porosity, pH, nutrient concentrations and the distribution of soil aggregates, which are clusters of mineral particles and organic matter that help determine how securely carbon is stored.

The strongest increase occurred under no-tillage with the highest fertilizer rate. In the topsoil, SOC reached 14.57 grams per kilogram, 22.0% higher than in the no-tillage control. In the subsoil, SOC rose to 8.75 grams per kilogram, representing a 93.2% increase. The result is particularly notable because carbon accumulation below the surface is usually difficult to achieve over a single growing season. Deeper soil carbon is often constrained by limited organic inputs, high compaction and slow biological activity, making the response observed in this experiment unusually large.

The researchers attribute the improvement to several processes operating at once. Straw supplied carbon-rich material, while the microbial fertilizer added both organic matter and microorganisms capable of transforming complex residues. No-tillage reduced physical disruption and helped preserve soil aggregates. These aggregates can enclose organic compounds within small pores, limiting their exposure to decomposing organisms and oxygen. In effect, the soil structure acts as a form of physical carbon protection. Surface straw may also reduce evaporation, moderate soil temperature and gradually release carbon compounds as it decomposes.

The results also exposed an important trade-off between carbon accumulation and soil structure. No-tillage generally produced the greatest proportion and stability of macroaggregates, the larger soil clusters that are particularly important for protecting organic carbon. Plough tillage, however, helped relieve compaction and promoted carbon accumulation in the subsoil, probably because it physically moved straw and fertilizer deeper into the profile. That benefit came at a cost: repeated soil disturbance frequently weakened macroaggregate stability, potentially leaving stored carbon more vulnerable to decomposition. Rotary tillage reduced topsoil bulk density and stimulated several biological processes, but its stronger enzyme activity did not consistently result in higher SOC.

To understand the mechanisms behind the changes, the team analysed four enzymes involved in carbon decomposition: α-glucosidase, β-glucosidase, cellobiohydrolase and endo-1,4-β-xylanase. These enzymes help microorganisms break down cellulose, hemicellulose and other plant-derived compounds. The researchers also examined microbial biomass carbon and used correlation-network analysis to identify relationships among biological, chemical and structural properties. In the topsoil, SOC was closely linked to microbial indicators and aggregate characteristics. In the subsoil, physical and chemical constraints appeared to exert a stronger influence, showing that carbon management may require different strategies at different depths.

The scientists caution that the findings represent only one year of field observations. A rapid increase in SOC does not automatically mean that carbon will remain stored for decades, and the experiment did not trace the survival or activity of the individual microbial strains added through the fertilizer. Longer-term studies will be needed to determine whether the carbon gains persist, how much carbon is held in stable fractions, and whether the treatment improves maize yields under different weather conditions. Even so, the study offers a potentially powerful blueprint for rebuilding degraded albic soils: disturb the soil less, keep crop residues in place and supply enough organic material to support sustained microbial activity. If confirmed over longer periods and across broader regions, the approach could improve soil resilience while helping agriculture contribute to carbon storage.

Subject of Research: Not applicable

Article Title: Tillage methods and microbial fertilizers synergistically enhance soil organic carbon concentration in albic soil

News Publication Date: 28 May 2026

Web References: https://www.maxapress.com/aee; https://doi.org/10.48130/aee-0026-0013

References: Fan, Wei, Cai, Hongguang, et al. “Tillage methods and microbial fertilizers synergistically enhance soil organic carbon concentration in albic soil.” Agricultural Ecology and Environment. DOI: 10.48130/aee-0026-0013

Image Credits: Agricultural Ecology and Environment

Keywords

Soil organic carbon, albic soil, no-tillage, straw retention, microbial organic fertilizer, soil aggregates, carbon storage, sustainable agriculture, soil health, climate change mitigation